Hydrocephalus, and our people usually say “water in the brain” is still a big difference, “water in the brain” generally describes the person to do things a little stupid, no brain, so that the brain into the water. The normal human brain there is water, it is called cerebrospinal fluid, is part of the normal composition of the human body, is a colorless and transparent liquid, exists in the ventricles of the brain and the subarachnoid neck, encircling the entire brain and spinal cord. It plays a protective role for the brain and spinal cord and serves to remove metabolites and inflammatory exudates like lymphatic fluid from other parts of the body. So since there is cerebrospinal fluid, or water, in a normal person’s brain, what is meant by hydrocephalus? This needs to start from the circulation of cerebrospinal fluid: cerebrospinal fluid is mainly produced from the choroid plexus within the lateral ventricles, the third ventricle and the fourth ventricle. The choroid plexus of the two lateral ventricles is the most abundant and produces the most cerebrospinal fluid, which flows into the third ventricle through the interventricular foramen, and then through the midbrain duct into the fourth ventricle. The cerebrospinal fluid produced by the choroid plexus of each ventricle converges to the fourth ventricle and flows into the subarachnoid space of the brain and spinal cord through the median and lateral foramina of the fourth ventricle. Finally, cerebrospinal fluid leaks back into the superior sagittal sinus via the arachnoid granules adjacent to the sagittal sinus, allowing the cerebrospinal fluid to flow back into the venous system. Cerebrospinal fluid is produced at a rate of 0.3 ml/min, with a daily secretion of 432 ml, and a normal adult has 130 ml of clear cerebrospinal fluid. Therefore, when there is an increase in the production of cerebrospinal fluid by the intraventricular choroid plexus, and/or impaired circulation and absorption, an abnormal accumulation of cerebrospinal fluid within the skull, which enlarges the ventricular system and/or the subarachnoid space, is a condition called hydrocephalus.